Optical device for use in an augmented reality or virtual reality device

ABSTRACT

An optical device or display is disclosed for use in an augmented reality or virtual reality device. The display includes a waveguide (2), an output element (4) and a plurality of input diffraction gratings (6, 8, 10, 12). Light from a plurality of projectors (16, 18, 20, 22) is diffracted by the input gratings (6, 8, 10, 12) so that it is coupled into the waveguide (2) by total internal reflection. The input gratings (6, 8, 10, 12) are provided in a staggered configuration in relation to the output element (4), with respect to a y-axis. Each input grating is adjacent another input grating that has a different separation distance from the output element (4). This can improve the evenness of illumination from the output element (4).

The present invention relates to an optical device for use with anaugmented reality or virtual reality device. In particular, theinvention relates to a wide screen display for an augmented realitydevice such as a head-up display.

In an augmented reality device a transparent waveguide is provided infront of a user's eye or eyes. A light projector transmits light towardsthe waveguide. Light can be coupled into the waveguide by an inputdiffraction grating. Light then propagates within the waveguide by totalinternal reflection and an output diffraction grating couples light outof the waveguide and towards a viewer. In use, a viewer can see lightfrom their external environment, transmitted through the transparentwaveguide, as well as projected light from the projector. This canprovide an augmented reality experience. These devices can be used inhead-up displays in a wide variety of applications, including industrialand automotive.

WO2016/020643 describes an optical device for expanding input light intwo dimensions in an augmented reality display. In this arrangement aninput diffractive optical element is configured to couple input lightinto a waveguide and two diffractive optical elements are overlaid onone another in or on the waveguide. The lines in each of the overlaiddiffractive optical elements are symmetrically angled with respect torays from the input diffraction grating. Each of the overlaiddiffractive optical elements can receive light from the inputdiffractive optical element and couple it towards the other diffractiveoptical element in the pair, which can then act as an output diffractiveoptical element, coupling light out of the waveguide towards a viewer.In this way the optical device can achieve two-dimensional expansion ofan input light source while simultaneously coupling light out of thewaveguide so that it can be viewed by a user.

It would be desirable to use the technology described in WO2016/020643in wide screen augmented reality displays. One challenge in developingsuch a display is to ensure that outcoupled orders can be providedevenly. An object of the present invention is to provide an arrangementthat addresses this challenge.

According to an aspect of the invention there is provided an opticaldevice or display for use in an augmented reality or virtual realitydevice, comprising: a waveguide; a plurality of input diffractiveoptical elements configured to couple light into the waveguide; anoutput element configured to receive light from the plurality of inputdiffractive optical elements in the direction of a first axis, whereinthe output element includes two diffractive optical elements overlaid onone another in or on the waveguide, wherein each of the two diffractiveoptical elements is configured to receive light from the inputdiffractive optical element and couple it towards the other diffractiveoptical element which can then act as an output diffractive opticalelement providing outcoupled orders towards a viewer; wherein theplurality of input diffractive optical elements are provided at at leasttwo respective positions with respect to the first axis.

In this way, light from respective input diffractive optical elementscan encounter the output element at different positions with respect tothe first axis. This can advantageously improve the evenness with whichoutcoupled orders can be provided towards a viewer. Preferably, forlight from a first input diffractive optical element, outcoupled ordersdo not coincide with outcoupled orders for light from a second inputdiffractive optical element.

Preferably first and second separation distances are provided on thefirst axis between the output element and respective input diffractiveoptical elements. In this way, a gap can be provided between an inputdiffractive optical element and the output element. In this way, lightfrom the input diffractive optical element can totally internallyreflect in the waveguide between the input diffractive optical elementand the output element. It is conceivable that the first or secondseparation distance could be zero in some embodiments. In anotherarrangement, one of the first and second separation distances isapproximately equal to the total internal reflection period in thewaveguide.

The plurality of input diffractive optical elements may be provided in astaggered configuration so that adjacent input diffractive opticalelements are provided in first and second positions with respect to thefirst axis. In some arrangements, therefore, first and second separationdistances may be provided sequentially for input diffractive opticalelements along the width of the waveguide. Advantageously this can allowgaps between outcoupled orders created from a first input diffractiveoptical element to be filled by outcoupled orders created from anadjacent input diffractive optical element. In some embodiments theremay be more than two separation distances for the input diffractiveoptical elements.

Light is preferably configured to travel from the plurality of inputdiffractive optical elements towards the output element by totalinternal reflection in the waveguide, and a total internal reflectionperiod may be provided. The difference between the at least tworespective positions with respect to the first axis is preferablydifferent to the total internal reflection period. Thus, a difference inphase can be established between the outcoupled orders for light fromthe respective input diffractive optical elements. This canadvantageously improve the evenness of the outcoupled orders in theoutput element.

The difference between the at least two respective positions withrespect to the first axis may be approximately half of the totalinternal reflection period. In this way, the outcoupled orders can beprovided substantially out of phase with one another in the outputelement.

The total internal reflection period may be related to the thickness ofthe waveguide as well as the angle with which light is diffracted by theinput diffractive optical elements. This may also be related to theangle with which light is provided to the input diffractive opticalelement.

The two overlaid diffractive optical elements in the output element maybe provided in or on the waveguide in different planes. The two overlaiddiffractive optical elements may be provided on opposing surfaces of thewaveguide. The two overlaid diffractive optical elements may be providedin substantially the same plane in the waveguide.

In a preferred arrangement the two overlaid diffractive optical elementscan be provided in a photonic crystal.

Embodiments of the invention are now described, by way of example, withreference to the drawings, in which:

FIG. 1 is a schematic plan view of a display or optical device in anembodiment of the invention;

FIG. 2 is a side view of the display shown in FIG. 1; and

FIG. 3 is an end view of the display shown in FIG. 1.

FIGS. 1-3 show a display or optical device comprising a waveguide 2, anoutput element 4 and a plurality of input diffraction gratings 6, 8, 10,12. The waveguide 2 has a first surface 3 and a second surface 5. Inthis example the input diffraction gratings 6, 8, 10, 12 are provided onthe first surface 3. A plurality of projectors 16, 18, 20, 22 providelight to the input gratings 6, 8, 10, 12 along a z-axis, referring to aCartesian reference frame. Light from the projectors 16, 18, 20, 22 isdiffracted by the input gratings 6, 8, 10, 12 in the direction of they-axis so that it is coupled into the waveguide 2 by total internalreflection. Light from the input gratings 6, 8, 10, 12 travels withinthe waveguide 2 by total internal reflection until it encounters theoutput element 4.

The output element 4 comprises two diffractive optical elements that areoverlaid on one another in or on the waveguide 2. The lines of each ofthe overlaid diffractive optical elements are symmetrically angled withrespect to the y-axis and the rays from respective input gratings 6, 8,10, 12. Each of the overlaid diffractive optical elements can receivelight from an input grating and couples it towards the other diffractiveoptical element in the pair, which can then act as an output diffractiveoptical element, coupling light out of the waveguide towards a viewer.In this way, and as explained in WO2016/020643, the output element 4 canachieve two-dimensional expansion of an input light source whilesimultaneously coupling light out of the waveguide 2 so that it can beviewed by a user.

Light can either be diffracted or transmitted on first interaction withthe output element 4. Thus, a proportion of the light received from eachinput grating 6, 8, 10, 12 continues to be totally internally reflectedwithin the waveguide 2 until its next interaction with the diffractivestructures of the output element 4. This is apparent from FIG. 2, whichshows propagation of the transmitted component by total internalreflection in the waveguide 2.

In FIG. 2 the rays are shown as if the diffractive structures for theoutput element 4 are located on the first surface 3 of the waveguide 2.This is possible, but they could also be located on the second surface5. In another arrangement, in particular in the case of a photoniccrystal, the diffractive structures could be provided in the interior ofthe waveguide 2.

The input gratings 6, 8, 10, 12 are provided in a staggeredconfiguration in relation to the output element 4, with respect to they-axis. The first input grating 6 is separated from the output element 4by a first distance, d₁, in the direction of the y-axis. The secondinput grating 8 is separated from the output element 4 by a seconddistance, d₂, in the direction of the y-axis. The first and seconddistances are used in turn for input gratings across the width of thewaveguide 2. Thus, each input grating is adjacent another input gratingthat has a different separation distance from the output element 4.

Diffracted rays from one of the input gratings on the first surface 3 ofthe waveguide are reflected by the second surface 5 of the waveguide 2,and then travel back towards the first surface 3. A total internalreflection period, p, may be defined as the distance along the y-axisbetween successive points at which the rays interact with the firstsurface 3 or the second surface 5. The period, p, is related to thethickness, t, of the waveguide 2. The period, p, is also related to theangle at which rays are diffracted from the input gratings 6, 8, 10, 12.

The difference between the first and second differences, d₂−d₁, ischosen as half of the total internal reflection period, p/2. In thisway, outcoupled orders from rays emanating from adjacent input gratingscan be provided out of phase with one another. This is achieved becauserays from a first input grating 6 are at a first surface 3 of thewaveguide at the same point on the y-axis as rays from a second inputgrating 8 are at the second surface 5 (and vice-versa).

Light is expanded in the x-y plane when it encounters the output element4, and rays are coupled out of the output element 4 in the z-axis,towards a viewer. Light is directed from the input gratings 6, 8, 10, 12in the y-axis towards the output element 4. Rays fan out from an initialpoint of contact with the output element 4 in a v-shaped cone. Asexplained in WO2016/020643, at each point of interaction, rays can bediffracted or coupled out of the waveguide 2 towards a viewer. FIG. 1 isa schematic diagram showing the points at which rays in v-shaped conesoriginating in first and second input gratings 6, 8 are coupled out ofthe waveguide 2. Outcoupled orders are provided in positions that areout of phase from one another, when considering rays emanating fromfirst and second respective input gratings 6, 8. Thus, where thev-shaped cones intersect, gaps in the outcoupled orders originating fromthe first input grating 6 can be filled by outcoupled orders originatingfrom the second input grating 8. Advantageously, this can improve theevenness of illumination from the output element 4. The output element 4can be used in a wide screen augmented reality display, such as ahead-up display.

1. An optical device for use in an augmented reality or virtual realitydevice, comprising: a waveguide; a plurality of input diffractiveoptical elements configured to couple light into the waveguide; anoutput element configured to receive light from the plurality of inputdiffractive optical elements in the direction of a first axis, whereinthe output element includes two diffractive optical elements overlaid onone another in or on the waveguide, wherein each of the two diffractiveoptical elements is configured to receive light from the inputdiffractive optical element and couple it towards the other diffractiveoptical element which then acts as an output diffractive optical elementproviding outcoupled orders towards a viewer; wherein the plurality ofinput diffractive optical elements are provided at at least tworespective positions along the first axis which are different to oneanother so that first and second separation distances are provided inthe direction of the first axis between the output element andrespective input diffractive optical elements.
 2. The optical device ofclaim 1, wherein the plurality of input diffractive optical elements areprovided in a staggered configuration so that adjacent input diffractiveoptical elements are provided in first and second positions along thefirst axis.
 3. The optical device of claim 1, wherein light isconfigured to travel from the plurality of input diffractive opticalelements towards the output element by total internal reflection in thewaveguide, and a total internal reflection period is provided, andwherein the difference between the at least two respective positionsalong the first axis is different to the total internal reflectionperiod.
 4. The optical device of claim 3, wherein the difference betweenthe at least two respective positions along the first axis isapproximately half of the total internal reflection period.
 5. Theoptical device of claim 1, wherein the two overlaid diffractive opticalelements in the output element are provided in or on the waveguide indifferent planes.
 6. The optical device of claim 5 wherein the twooverlaid diffractive optical elements are provided on opposing surfacesof the waveguide.
 7. The optical device of claim 5, wherein the twooverlaid diffractive optical elements are provided in substantially thesame plane in the waveguide.
 8. The optical device of claim 1, whereinthe two overlaid diffractive optical elements are provided in a photoniccrystal.